This invention relates to an intake and exhaust structure for a V-type engine and more particularly to an improved exhaust and intake system for an outboard motor embodying a V-type engine.
The requirement of compact construction for the powerhead of outboard motors is well known. It is desirable to maintain the powerhead as compact as possible in order to avoid unnecessary obstruction of the operator's view. In addition, it is desirable to maintain a relatively low center of gravity of the powerhead so as to assist in the tilt and trim operation and also to ensure against intrusion of the powerhead into the body of the watercraft.
With the increased emphasis on larger watercraft and more powerful engines, resort has been had to the use of multiple cylinder engines so as to suit the requirements of the watercraft and operators. However, when multiple cylinder engines are employed, the problems of maintaining a compact construction are magnified. In order to provide a more compact arrangement for multiple cylinder engines, it has been proposed to employ V-type engines in outboard motors.
However, there is a another facet of outboard motor construction that makes the design of the powerhead difficult. This is the fact that the engine is normally positioned so that its output shaft rotates about a vertically disposed axis rather than horizontally disposed as with most vehicle applications. This presents certain problems, particularly in conjunction with the design of the induction and exhaust system for the engine. These problem become particularly difficult in conjunction with V-type engines.
In addition to the aforenoted problems, there is recently an emphasis towards the use of 4-cycle engines as the power plant of an outboard motor. Four-cycle engines avoid some of the emission problems associated with 2-cycle engines. However, the 4-cycle engines present additional problems not normally associated with 2-cycle engines due to the fact that the induction and exhaust ports of the engine are formed in the cylinder head normally with a 4-cycle engine while they are formed generally in the cylinder block with a 2-cycle engine.
In the exhaust systems for outboard motors, the exhaust gases are generally transferred downwardly from the powerhead to the driveshaft housing lower unit wherein a silencing system is provided that includes an underwater high speed exhaust gas discharge. The driveshaft housing lower unit permits the provision of silencing devices such as expansion chambers and the like since the space available there is normally greater than that in the powerhead. However, the downward routing of the exhaust gases provide certain problems, particularly in conjunction with V-type engines.
With a V-type engine, it is the normal practice to provide the exhaust manifolds on the outer periphery of the engine and the induction system is provided in the valley between the cylinder banks. However, this placement has certain disadvantages.
In the first instance, to route the exhaust gases downwardly into the driveshaft housing, it is necessary to provide, with a V-type engine, a pair of exhaust manifolds one on the outside of each cylinder bank. However, these exhaust gases normally are delivered to an exhaust pipe that is positioned centrally in the driveshaft housing so as to maintain a compact configuration and to avoid interference with the driveshaft which is driven by the engine output shaft. Hence, when the exhaust manifolds are on the outside of the cylinder banks, it is necessary to pass them under the cylinder banks to a common discharge opening positioned beneath the engine. This necessitates elevation of the engine to provide the collection beneath it and raises the center of gravity.
In addition, when the exhaust manifolds are on the outside of the cylinder bank and the induction system is in the valley between the cylinder banks, the intake manifolding must extend rearwardly in the powerhead beyond the cylinder banks to the air inlet device. If carburetors are employed as charge formers, the induction system is further lengthened thus increasing the overall size of the powerhead and specifically the engine thereof.
It is, therefore, a principal object of this invention to provide an improved exhaust and inlet system for a V-type engine utilized in an outboard motor so as to provide a more compact and lower overall construction.
It is a further object of this invention to provide an improved exhaust system for a V-type engine for an outboard motor that will permit central discharge of the exhaust gases and a compact arrangement.
It is a further object of this invention to provide an improved induction system for a V-type engine for use in an outboard motor that will provide a compact assembly and will not increase the fore and aft length of the engine.